Physical Sciences Division Research Highlights

January 2013

A Pathway for Protons

Efficient delivery to material's center turns oxygen cleanly into water

Scientists from the Center for Molecular Electrocatalysis have built two iron-based compounds that help protons move from the exterior to where they are needed. Once delivered, the protons bond with molecular oxygen and create water.

Results: Pushing protons around may sound like a small
task, but it is a big part of energy independence for the United States. Moving
four relatively large protons to where they are needed is easier if you build a
path, as is being done by scientists at the Center
for Molecular Electrocatalysis. The research team has built two iron-based compounds
that help protons move from the exterior to where they are needed. Once
delivered, the protons bond with molecular oxygen, O2, and create
water. In previous compounds, the protons often don't arrive in time or go to
the wrong place, which leads to forming the unwanted byproduct hydrogen
peroxide (H2O2). The new compounds direct the protons in
ways that help separate the two oxygen atoms in O2, and thereby drives
the reaction to completion.

"While water is the end product, it is not the goal of
our work. These studies show that we can take the knowledge that the Center for
Molecular Electrocatalysis has learned for reactions that move two protons and
apply that knowledge to the challenge of relaying four protons," said Dr. James Mayer,
an expert in proton-coupled electron transfer reactions and a professor at the University of Washington, who led this
research.

Why It Matters: Understanding
how to move protons efficiently lets scientists design new materials that can
turn electrons generated by wind turbines and solar farms into fuels, creating easily
transported, use-any-time alternatives to coal and oil.

"We want to generate as much power as we can when the
conditions are right and store the energy," said Dr. Monte Helm, Deputy
Director for the Center for Molecular Electrocatalysis. "This research is
directly related to storing that energy in chemical bonds, so we can get the
energy out at a future time, when necessary."

Methods: The
researchers began with a ruthenium compound. They experimented with the best
location to place the relay in the material to deliver protons, which move by a
different route than the electrons needed in the reaction. The researchers went
on to design two iron-based, selective compounds that work quickly and
efficiently through the entire oxygen reduction reaction, turning oxygen into
water.

"It's a proof of concept that we can do this with cheap
metals and provides promise for moving the science forward," said Helm.

What's Next? At
the Center, researchers are continuing to improve the compounds' oxygen
reduction performance, working to make it faster, to produce less of the unwanted
hydrogen peroxide, and to make it more efficient. They are also determining if
the new insights they've developed can be applied to a reaction that requires
the movement of six protons.

Acknowledgments:

Sponsors: This
work is supported as part of the Center for Molecular Electrocatalysis, an
Energy Frontier Research Center funded by the U.S. Department of Energy, Office
of Science, Office
of Basic Energy Sciences.

Research Team: Colin T. Carver, Benjamin D. Matson, Tristan A.
Tronic, Werner Kaminsky, Michael K. Coggins, and James M. Mayer, Center for
Molecular Electrocatalysis. Team members are from University of Washington, a
partner in the center. They collaborated with Amber Von Ruden, Jenny Y. Yang, and
Simone Raugei of PNNL.